(1) Field of the Invention
The present invention relates to an image forming apparatus, and in particular, to a technology of preventing water droplets generated by condensation, in the image forming apparatus, of water vapor generated at a fixing unit from contacting a sheet.
(2) Description of the Related Art
An image forming apparatus such as a printer and a copier is commonly provided with a fixing unit for heat-fixing a toner image onto a recording sheet (hereinafter referred to simply as a “sheet”).
A fixing unit in a common image forming apparatus applies heat to a sheet to perform heat-fixing. When heat is applied to a sheet, moisture contained in the sheet is discharged, which results in the generation of water vapor. When water vapor is generated in such a manner at the fixing unit, the water vapor rises upwards in the image forming apparatus and condenses at an inner surface of an outer cover of the image forming apparatus. When condensation of water vapor takes place at the inner surface of the outer cover, there is a risk of the water vapor dropping onto a sheet being conveyed in the image forming apparatus in the form of water droplets. This leads to problems such as the formation of creases in the sheet and the decrease in quality of an image printed on the sheet.
In view of such problems, a proposal is being made of an image forming apparatus that prevents water droplets from dropping onto a sheet by being provided with a mechanism for receiving water droplets falling downwards from an inner surface of an outer cover of the image forming apparatus. More specifically, such a mechanism is disposed with respect to a guide member that is located relatively higher (hereinafter referred to as an upper guide member) among a pair of guide members forming a sheet conveyance path in the image forming apparatus.
For instance, Japanese Patent Application Publication 2006-322994 discloses a structure (a mechanism for collecting water droplets) where the upper guide member includes: a water droplet collection container (a water droplet accumulation portion) that is located above a sheet passing region; and a plate-like water droplet guiding member (a water droplet-receiving plate portion) that receives water droplets dropping thereon from the inner surface of the outer cover and guides the water droplets to the water droplet collection container. The water droplets collected by the water droplet collection container evaporate naturally, and are discharged to the outside of the image forming apparatus.
Further, Japanese Patent Application Publication No. 5-35135 discloses a fixing device having an upper cover that is provided with a water droplet reception/accumulation portion. The water droplet reception/accumulation portion is composed of a water droplet receiver that receives water droplets generated on an inner surface of the upper cover and a water droplet accumulator that accumulates the water droplets received by the water droplet receiver. Further, the upper cover is provided with a shape for guiding the water droplets towards the water droplet reception/accumulation portion.
In addition, Japanese Patent Application Publication No. 2007-304161 discloses a cooling device that includes a fixing device, a cooling portion, and a moisture transporting means. The cooling portion is arranged so as to be in contact with or in close proximity to the fixing device. Further, the surface of the cooling portion is water repellent, and moisture attaching to the surface of the cooling portion is transported to a predetermined location by the moisture transporting means.
However, in a conventional image forming apparatus provided with a water droplet collection container (i.e., a water droplet reception/accumulation portion), there is a risk of water droplets overflowing from the water droplet collection container in the worst-possible case. Here, the worst-possible case refers to, for instance, a case where continuous printing of an enormous number of sheets is performed. When an enormous number of sheets are continuously printed, the amount of water vapor generated at the fixing unit increases. This further results in the amount of water droplets collected by the water droplet collection container increasing and possibly exceeding the amount of water droplets naturally evaporating from the water droplet collection container, which leads to water droplets overflowing from the water droplet collection container. In such a case as described above, the water droplets flowing out from the water droplet collection container may drop onto a sheet being conveyed in the image forming apparatus. This gives rise to problems such as the formation of creases in the sheet and the decrease in quality of an image printed on the sheet